1. Technical Field
The invention relates to a profiled bar, in particular a load-bearing, prism-shaped profiled bar. The invention furthermore relates to uses for such a profiled bar and to a method for its production in.
2. Prior Art
The profiled bars referred to here are profiled, elongate objects which in particular can be subjected to high loads and have a defined elasticity. Profiled bars of this type are usually formed from a matrix of thermosetting or thermoplastic material (plastic matrix), the plastic matrix being reinforced by fibres, which is also to be understood as meaning fibre strands. These fibres are usually synthetic fibres, which are relatively expensive. In many cases, the synthetic fibres used are glass and mineral fibres. However, these are not environmentally compatible. In particular, such profiled bars become increasingly difficult to dispose of as the proportion of glass and mineral fibres increase.
In view of the above, the invention is based on the object of providing a profiled bar, a method for its production and preferred uses of a profiled bar of this type, with a view to achieving good environmental compatibility, while the other required properties are to be maintained as far as possible.
A profiled bar for achieving this object has the features of claim 1. According to this claim, both synthetic fibres and natural fibres (which is also intended to mean synthetic fibre strands and/or natural fibre strands, without these being expressly mentioned) are provided in the plastic matrix. The synthetic fibres are preferably based on hydrocarbons. These synthetic fibres are easy to dispose of. Natural fibres are generally regarded as environmentally friendly. This is because they can be obtained from regrowing raw materials and can also be disposed of. in an environmentally friendly manner. However, they cannot be subjected to the same level of load as synthetic fibres. The use according to the invention of both types of fibre has shown that, despite the deployment of a certain amount of natural fibres, it is possible to form profiled bars which with regard to the mechanical properties are equivalent to profiled bars which are reinforced-only by synthetic fibres.
According to a preferred refinement of the invention, the synthetic fibres (or synthetic fibre strands) are only assigned to selected cross-sectional areas of the profiled bar, preferably to outer cross-sectional areas. As a result, the synthetic fibres, which have a high tensile strength, are situated at areas of the profiled bar which are subjected to particularly high loads, where they can unfurl their full action. As a result, the particular mechanical properties of the synthetic fibres are utilized to the maximum possible extent. The natural fibres arranged in other cross-sectional areas can then be situated in those cross-sectional areas of the profiled bar which are subjected to lower levels of load, with the result that the natural fibres are only subjected to loads which are within the scope of their lower strength.
It is possible for the natural fibres to be distributed uniformly or non-uniformly over the entire cross-sectional area of the profiled bar which is left free by the synthetic fibres. However, it is also conceivable for the natural fibres likewise only to be assigned to specific cross-sectional areas of the profiled bar, so that the profiled bar has cross-sectional areas which contain neither synthetic fibres nor natural fibres. These may, for example, be central cross-sectional areas of the profiled bar which are substantially free from load. Moreover, by assigning the natural fibres and the synthetic fibres to selected cross-sectional areas, it is possible to achieve targeted spring properties of the profiled bar.
Preferably, at least the synthetic fibres run continuously in the longitudinal direction of the profiled bar, in the form of synthetic fibre strands, i.e. they are generally in the form of endless fibres. By contrast, the natural fibres are generally of endless length. They are therefore preferably twisted into yarns or are used as carded or nonwoven fabric.
If continuous (endless) strands of synthetic fibres are provided in the profiled bar, the individual strands of the plastic fibres are preferably arranged in the plastic matrix without any twisting whatsoever. This makes it easy to impregnate or saturate the synthetic fibre strands with the plastic matrix. Moreover, this imparts improved tensile and flexural strength to the profiled bar.
The synthetic fibre strands are predominantly used entirely as endless strands which extend continuously over the entire length of the profiled bar. However, it is also conceivable to employ a combination or mixture of endless synthetic fibre strands and synthetic fibre strands of finite length, the latter preferably in the form of a carded fabric.
According to a preferred design of the profiled bar according to the invention, the synthetic fibres and the natural fibres are preferably completely embedded in the plastic matrix. In this way, the fibres or fibre strands are protected inside the profiled bar. Furthermore, the synthetic fibres and the natural fibres are impregnated or saturated by the plastic matrix. In this way, the properties of the fibres are optimally utilized and delamination phenomena are effectively avoided.
Natural fibres which may be considered are preferably those which are formed from hemp, flax, sisal, cellulose or ramie. It is also conceivable to use combinations of the said natural fibres. These materials are available in sufficient quantities and at low cost, since they are regrowing raw materials. The said natural products are relatively lightweight, so that they practically do not increase the weight thereof.
Synthetic fibres which may preferably be considered are those based on hydrocarbons, in particular carbon fibres, aramid fibres or aramid combinations, which can be disposed of in an environmentally friendly manner, in particular by thermal recycling, so that they are not significantly contradictory to the desired environmental compatibility. In some cases, they also allow downcycling. The said synthetic fibre materials may also be used in mixed form, for example by carbon fibres and aramid fibres, preferably in each case in the form of strands, being present in the profiled bar. The said synthetic fibres have a relatively high tensile strength, so that partial substitution thereof by natural fibres does not significantly impair the load-bearing capacity and elasticity of the profiled bars.
The plastic matrix may comprise a thermosetting or thermoplastic material. This may be an epoxy system, polyurethane or polyester. It is preferable to use a matrix made from a thermosetting material, which ensures that the profiled bar is easy to produce, in particular that the fibres and fibre strands can be impregnated or saturated successfully.
The profiled bar according to the invention can preferably be used to form sprung bars, in particular those which are used for furniture for sitting and/or lying on and bottom sprung supports for furniture for sitting and/or lying on, preferably slatted frames. With these sprung bars, it is particularly important to achieve good environmental compatibility, since the products for which they are used are increasingly being purchased under consideration of environmental aspects.
According to the invention, the profiled bar may furthermore be used for longitudinal members and/or frames for furniture, in particular for furniture for sitting and/or lying on, preferably beds and/or slatted frames. Finally, it is conceivable for the profiled bar according to the invention to be used to at least partially form frames for rehabilitation aids.
During the production of the profile or the profiled bar, the procedure is such that the synthetic and natural fibres, preferably fibre strands and/or fibre webs, are passed through at least one impregnation member, where they are fed with free-flowing plastics material in order to form the plastic matrix. Passing at least some endless synthetic fibres and natural fibres which are usually of endless length through the impregnation member at the same time leads to the process forces required to pull the fibres through, whether they be in the form of strands or webs or combinations thereof, being absorbed by the endless synthetic fibres which have a high load-bearing capacity, while the natural fibres pass through substantially without being exposed to load or with a lower level of load, and therefore there is no risk of the natural fibres, which have a lower tensile strength, being torn during the production process.
Further subclaims relate to advantageous refinements of the method.